Test: cts-scheduler: Create output subdirs if they don't exist

Since commit 4becd5d, if --out-dir is specified, all the required
subdirectories must already exist.

With this commit, we automatically create any missing subdirs, provided
that <out-dir> itself exists.

Since we're creating the subdirectories ourselves now, we also give .out
files and .valgrind files their own subdirs.

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>